Numerical Investigation of Droplet Impact on the Surface by Multiphase Lattice Boltzmann Flux Solver

The dynamic behaviors of the micro-sized water droplet collision onto the wings of the aircraft are essential to the flight safety. The details on the small droplet in the airflow in contact with the aircraft wing surface play a quite important role in the ice accretion process. In this paper, multiphase lattice Boltzmann flux solver coupled with phase field method is applied to simulate the water droplet impact onto the solid hydrophilic/hydrophobic surface to further understand the interactions between droplet and surface at mesoscopic level. The reliability and accuracy of the numerical method is validated by the comparison with experimental data and computational results in other literatures, which shows that the solver is capable of predicting the droplet dynamic behaviors. Then, the effects of different physical parameters such as impact velocity, droplet diameter, surface contact angle and impact inclination angle, are systematically studied. The computational results reveal that when the collision is normal to the surface, the water droplet may experience spreading phase, recoiling phase as well as rebounding phase and finally shows the adhesion state or detachment from the surface. The higher velocity and larger diameter contribute to spread the droplet wider and jump higher during the droplet impact process. And a shorter physical time is taken to reach the spreading factor maximum for higher velocity while it is opposite for the droplet with a lager diameter. Moreover, the whole evolutionary process of smaller-sized droplet is accelerated and smaller diameter as well as higher contact angle of the surface advances the droplet detachment from the hydrophobic surface. It is also found that the surface with higher contact angle impedes the droplet spreading and removes the temporal lag of its performance in lifting up the upper end of droplet during recoiling phase and rebounding phase, which is distinct to the results of higher velocity and larger diameter. Besides this, droplet impact with an inclination angle causes reduction on the spreading factor maximum and jump height after detachment from the surface due to the decrease on the normal velocity of the droplet. And the increase of the tangential velocity accounts for the longer contact time with the surface for the droplet, and causes the difference of the spreading factors in spreading directions, which forms an oval contact area on the surface until the droplet detaches. The analysis and quantitative comparison of the temporal morphology evolutions of the micro-sized droplet in this paper help to reveal the interaction mechanism between the different-sized droplets and surfaces with different properties, which can be considered specially in the numerical prediction of the aircraft icing.